Effects of a native oxide layer on the carrier mobility and void formation at aluminum-induced crystallization of amorphous silicon

In the present study, the effects of the native oxide layer that forms between an amorphous Si (a-Si) layer and a microcrystalline Al (μc-Al) layer in the coating processes on the crystallizations of a-Si, the microstructure at the mixing layer [μc-Al and microcrystalline Si (μc-Si) at the a-Si layer], and the carrier mobility of the μc-Si+a-Si film produced by aluminum-induced crystallization are investigated. The effect of the μc-Al film on Si crystallization was also investigated by varying the thickness of the Al film in the specimens without a native oxide layer. The absence of a native oxide layer at the interface of the μc-Al and a-Si layers allowed Si crystallizations at a lower annealing temperature and a shorter annealing time, and increased the carrier mobility significantly. A sufficiently large μc-Al film thickness was required for Si crystallization in the specimens without a native oxide layer; however, an excessive thickness deteriorated the crystallization behavior. The native oxide layer detected using X-ray photoelectron spectroscope was a barrier for the penetration of μc-Al into the a-Si layer. Si crystallizations were often accompanied by voids of various sizes and densities. The carrier mobility generally decreased with increasing void size and density of voids.